In conventional hard disk drives, data is written in concentric circular tracks by a magnetic recording head which is positioned above a spinning disk. The magnetic recording head consists of a write head element which is used during writing, and a read head element which is used during reading. During writing, the position of the magnetic recording head above the disk is precisely controlled by a servomechanical feedback loop so that the written data tracks do not overlap. The width of each track is determined by the width of the write head element. The center-to-center spacing of each track (also known as the track pitch) is slightly larger than the track width, and is determined by the servomechanical control system which keeps the head properly positioned above the disk. Each track is separated from its neighbor by a guard band whose width is equal to the track pitch minus the track width. During read back, the read back element in the recording head is precisely positioned above a single track. The width of the read back element is usually equal to or smaller than the width of a written track, so that the read head element detects the signal from only that single track and not from neighboring tracks.
With these hard disk drives, each track may be randomly written at any time without disturbing the data on any of the other tracks. This ability to randomly update and access the data on the surface of the disk is an important characteristic of hard disk drives which is not shared by all data storage systems. However, it can be difficult to achieve high areal density in conventional hard disk drives which use rotary actuators so that the length of the write pole can be made as large as desired, because conventional recording schemes require the write head to be smaller in width than the track width, and of a length not much larger, to avoid writing on the adjacent tracks. The resulting small area of the writing pole limits the ability to obtain large write fields under the poletip. One approach to solve this problem would be to use near zero-skew actuators, but such actuators have a performance penalty associated with longer arms.
In U.S. Pat. No. 6,185,063, incorporated herein by reference, so-called shingled track writing is mentioned in which partially overlapping tracks are used. Specifically, with shingled track writing, data tracks are written such that each written track partially overlaps an immediately adjacent track that is contiguous to it, like shingles on a tiled roof. Thus, a first track is partially overwritten when a second track contiguous to the first is written, which in turn is partially overwritten when a third track contiguous to the second is written, and so on.
As recognized herein, unlike the conventional approach described above, the write head width advantageously can be significantly larger than the track pitch in shingled track writing, whereas the width of the read back head element can be slightly less than the track pitch so the read back head still detects signal from only a single track and not from neighboring tracks.
The present invention but not the above-referenced patent critically recognizes that although, for reasons discussed more fully below, shingled writing can result in higher data storage density, a consequence of shingled writing of adjacent tracks is that poorly written data from the side of a wide and long head can fall on already written data when the slider is skewed, i.e., oriented obliquely with respect to the data tracks. More specifically, when a “tall” write pole (a write pole having a thickness greater than the track pitch) is skewed in a longitudinal recording system, writing data in one track disturbs data written in an adjacent track. Since most of the write flux in longitudinal recording emanates at the leading edge of the write pole, the disturbance takes the form of a slight erasure of data in the adjacent track, and multiple write passes are required to erase adjacent data. In contrast, when a “tall” write pole is skewed in a perpendicular recording system, writing data in one track still disturbs data written in an adjacent track, but because significant write flux in perpendicular recording emanates from all portions of the write pole, only a single pass results in erasing data in adjacent tracks. In either case, data in adjacent tracks can be disturbed even when the track width of the write head is narrower than the track pitch. Having recognized these drawbacks, the solutions herein are provided.